An autocorrelator is an apparatus for measuring a short sub-picosecond pulse which cannot be directly measured by an optoelectronic apparatus. Supposing that a function with respect to a time of an electric field of an optical pulse is E(t), the autocorrelator generates an autocorrelation function represented by A(t)=∫|E2(t)E2(t−τ)|2dτ. Here, τ represents a delay time. Further, a time width of a pulse used in measurement is estimated using an autocorrelation function generated by the autocorrelator.
The autocorrelator includes an interferometer part for controlling a delay time by dividing a pulse in two, and a measurement part for measuring by generating a secondary harmonic wave with respect to the two generated pulses using a nonlinear optical medium.
FIG. 1 is a conceptual diagram of a conventional autocorrelator using a Michelson interferometer. The conventional autocorrelatormay use the Michelson interferometer 10. An optical pulse which is incidenton the Michelson interferometer 10 may bedivided into two pulses by a beam splitter 11. Here, the beam splitter 11 included in the Michelson interferometer 10 may divide a beam into beam splitter 11 included in the Michelson interferometer 10 may divide a beam into at angle of 90 degrees. The beam divided by the beam splitter 11 may be reflected by a reflective mirror 12. That is, the Michelson interferometer 10 may generate two pulses using two beam splitters 11 and four reflective mirrors 12. Further, the two pukes generated by the Michelson interferometer 10 may be converted into a secondary harmonic wave by passing through a secondary harmonic wave medium 20.
The autocorrelator using the Michelson interferometer 10 needs the two beam splitters 11 and the four reflective mirrors 12 in order to constitute a balanced interferometer. That is, since production of the autocorrelator and volume of the autocorrelator are determined by the Michelson interferometer, there are limitations in reducing production costs of the autocorrelator and decreasing the volume of the autocorrelator.